In the Global System for Mobile Communications/Enhanced General Packet Radio Service (GSM/EGPRS) Base Station System (BSS) protocol between the LLC (Logical Link Control) and RLC/MAC (Radio Link Control/Medium Access Control), the payload LLC Protocol Data Unit (PDU) is carried within the RLC data block, which has a fixed length. From a spectrum efficiency point of view, it is desirable to fill the RLC data block as far as possible. Therefore, delimiting these LLC Protocol Data Units (PDUs) within the RLC data block is necessary. RLC header Length Indicators (LI) are given in octets, depending on how many LLC PDU are carried in the same RLC data block. Similar problems occur in other protocol stacks, whether using an Open Systems Interconnection (OSI) or other common protocol stack known to those skilled in the art.
As an example of a delimiter problem, a special case occurs when the last LLC PDU fills the remaining octets of the RLC data block precisely. As a result, adding the LI octet would take the protocol data unit out of the RLC data block boundary, requiring another RLC block to carry the rest of the LLC PDU. In this case, two delimiters are required for one LLC PDU. This is a waste of capacity and may cost spectrum when services requiring a short Temporary Block Flow (TBF) is supported, such as with an internet application.